Effect of oxidation temperature on physical properties of polycrystalline β-Ga2O3 grown by thermal oxidation of GaN in O2 ambient from 900 to 1400 °C

Abstract

This study aimed to investigate the effect of oxidation temperature on the physical properties of β-Ga2O3 grown by thermal oxidation of GaN in the O2 ambient at high oxidation temperatures from 900 to 1400 °C. Notably, the analysis of the oxidation temperatures ranging from 1100 to 1400 °C remains unexplored in the other studies. The effects of the oxidation temperature on the physical properties were investigated via X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy (FESEM). At all oxidation temperatures, XPS results revealed oxygen deficiency. The top FESEM images indicated disordered nanocolumn structures on the surface of the oxide layer, which increased in abundance with oxidation temperatures exceeding 1100 °C. Energy-filtered high-resolution transmission electron microscopy images and the selected area electron diffraction patterns revealed that the top nanocolumns and the oxidized layer comprised polycrystalline β-Ga2O3. Additionally, the cross-sectional lamellae prepared through focused ion beam milling revealed an increase in the thickness of the β-Ga2O3 layer with oxidation temperature. To account for the variations in the oxide layer thickness, the oxidation temperatures were classified into two ranges of 900–1100 °C and 1100–1400 °C for calculating the activation energy. Moreover, this study assumed that the activation energy required for the oxidation process remained constant within each temperature interval. According to Arrhenius's model, the activation energy from 900 to 1100 °C was calculated to be 286.15 kJ/mol (2.97 eV). Furthermore, the activation energy from 1100 to 1400 °C was determined to be 111.33 kJ/mol (1.15 eV).